Dramatic reductions in surgical mortality for children with congenital heart disease (CHD) have enabled investigators to focus on factors affecting quality of life and neurologic morbidity. Patients with CHD are at significant risk of neurologic impairment from altered perfusion and hypoxemia. Brain ischemia can occur as a result of abnormal blood flow due to CHD, associated congenital anomalies, or issues related to modifiable factors in the intensive care unit. The broad objective of this concept proposal is to demonstrate that near infrared spectroscopy (NIRS) cerebral tissue oxygenation index (TOI) will identify significant cerebral ischemia and provide an opportunity for real-time intervention in the intensive care unit. Aim 1 will determine whether perioperative NIRS cerebral TOI differs between CHD patients versus normal newborns. Aim 2 will determine the association between NIRS cerebral TOI in the perioperative period with neurodevelopmental outcome and brain MRI findings. Neonates undergoing cardiac surgery requiring cardiopulmonary bypass will have NIRS monitoring preoperatively, intraoperatively and postoperatively. These neonates will also undergo pre- and postoperative brain MRI and formal neurodevelopmental testing. Neurodevelopmental follow up will occur at 6, 15, and 21 months. Longitudinal multiple linear regression models will be developed to evaluate whether neurodevelopmental changes and brain abnormalities on MRI are related to cerebral TOI in the perioperative period. If established as a predictor, then optimizing TOI will provide the basis for future interventional studies in the ICU to improve neurodevelopmental outcomes.